The inventors herein have recognized that the number of cycles completed by an engine during an engine shutdown can affect emissions on subsequent engine starts. Specifically, after fuel injection is stopped, the engine may continue to rotate, thus pumping lean gasses to the catalyst thereby increasing its oxidation state. Then, during subsequent restarts, the oxidized catalyst may perform less efficiently.
In one example, this can be addressed by a method for operating at least an intake and exhaust valve in a cylinder with a piston of an engine in a vehicle, comprising:
during conditions of an engine shut-down, maintaining at least one of the intake and exhaust valves in a closed position during a period, and during at least said period where said at least one valve is in said closed position: operating with the other of the intake and exhaust valve open, then closing the other of the intake and exhaust valve, and then opening the other of the intake and exhaust valve to generate braking torque to slow the engine.
It this way, it may be possible to reduce stopping engine stopping time and thereby pump fewer gasses through the catalyst. Further, other advantages may be obtained as discussed in detail below.